an evaluation of stabilized, water-based drilled cuttings and organic compost as potential sediment...
TRANSCRIPT
ECOLOGICAL E N G I N E E R I N G
ELSEVIER Ecological Engineering 5 (1995) 497-517
An evaluation of stabilized, water-based drilled cuttings and organic compost as potential sediment sources for
marsh restoration and creation in coastal Louisiana
Suzanne Kelley 1, Irving A. Mendelssohn *
Wetland Biogeochemistry Institute, Louisiana State University, Baton Rouge, LA 70803, USA
Received 21 November 1994; accepted 6 April 1995
Abstract
The influence of various substrate types (drilled cuttings, compost, 50/50 mixture drilled cuttings/compost, and marsh sediment control) and soil fertilizers (macronutrients, mi- cronutrients, and unfertilized control) on growth of Spartina alterniflora and Sagittaria lancifolia and on soil chemistry were evaluated in greenhouse experiments. Substrate type and fertilizer amendment had significant effects on plant growth, with the two marsh species responding similarly. Substrate interstitial water pH levels appeared to have a direct effect on nutrient availability and subsequent plant growth. Poorest plant growth was observed in drilled cuttings, which had the highest pH level of the four substrates (mean = 10.4). Addition of compost to drilled cuttings decreased pH (mean = 8.4) and resulted in significantly greater total plant biomass. Compost and control sediments had the most neutral pH levels (combined mean = 7.3) and produced greatest total plant biomass.
Separate additions of macronutrients and micronutrients stimulated growth of both plant species. However, the simultaneous addition of macronutrients and micronutrients resulted in significantly greater plant biomass than macronutrient fertilization alone or unfertilized control substrates. These experiments demonstrated that when drilled cuttings were amended with organic compost, and especially maeronutrient and micronutrient fertilizers, plant growth levels were comparable to those observed in natural estuarine sediments.
* Corresponding author. I Present address: Louisiana Department of Natural Resources, Coastal Restoration Division, P.O.
Box 94396, Baton Rouge, LA 70804, USA.
Elsevier Science B.V. SSDI 0925-8574(95)00040-2
498 S. Kelley, I~. Mendelssohn /Ecological Engineering 5 (1995) 497-517
Keywords: Wetland ecology; Marsh restoration; Drilled cuttings; Louisiana; Spartina alterni- flora; Sagittaria lancifolia; Fertilization; pH
1. Introduction
Due to absence of riverine sediment inputs, local subsidence, eustatic sea level rise, and the resultant saltwater intrusion and submergence of coastal marshes, Louisiana is experiencing approximately 80% of the Nation's coastal wetland loss (Mendelssohn et al., 1983; Turner and Cahoon, 1987; Louisiana Coastal Wetlands Conservation and Restoration Task Force, 1993). Several studies suggest that direct sediment additions may be the best mitigation to deteriorating coastal wetlands (Baumann and DeLaune, 1981; Baumann et al., 1984; Mendelssohn and McKee, 1989; DeLaune et al., 1990; Nyman et al., 1990). Addition of sediments improves marsh stability and primary productivity by increasing marsh surface elevation and nutrient supply to plant communities and by decreasing poor soil physicochemical conditions and flooding stress to vegetation (DeLaune et al., 1990; Pezeshki et al., 1992; Wilsey et al., 1992). Within the past few years, the state of Louisiana has proposed and implemented several sediment diversion projects involving the Mississippi River and its distributaries. In addition, some marsh restoration and creation projects have been successfully executed using local bayou- and canal-dredged material as the primary sediment material for additions to the marsh surface (Louisiana Department of Natural Resources, 1990-1995).
The present study investigated use of two "novel" sediments as alternative, additional sources for marsh restoration. Cuttings from oil and gas drilling are considered to be an abundant solid waste by-product of t he industry. Drilled cuttings consist primarily of the rock or shale parent material being drilled and may be associated with varying amounts of drilling mud constituents (barite, organic thinners, polymers, lime, sodium hydroxide, clays, and native muds) depending on the location, depth, and type of formation being drilled (Gray and Darley, 1980). Following proper treatment of any potentially toxic constituents, however, drilled cuttings could be a valuable resource for use in sediment addi- tions to deteriorating marshes, potentially an ecologically sound alternative to costly disposal methods currently practiced. In order to provide a suitable sub- strate for growth of wetland vegetation, drilled cuttings, which have a high pH (10 to 10.5), may need to be amended with an organic component, such as terrestrial compost, and/or fertilizer to improve fertility.
The objective of this study was to determine if drilled cuttings and organic compost can support the survival and growth of dominant wetland vegetation. Three experiments were conducted which evaluated growth of dominant Louisiana salt marsh and fresh marsh plant species (Spartina alterniflora and Sagittaria lancifolia, respectively) and several soil physicochemical parameters in response to various substrate combinations involving drilled cuttings, organic compost, and fertilizer amendments.
S. Kelley, LA. Mendelssohn /Ecological Engineering 5 (1995) 497-517
2. Materials and methods
499
2.1. Sediment sources
In contrast to oil-based drilling fluids which are reported to have negative environmental effects (Davies et al., 1989), most water-based drilling fluid con- stituents are reported to be non-toxic to marine organisms (National Research Council, 1983). The drilled cuttings used in this study were associated with only water-based, minimal density (small amounts of barite and thinners) drilling fluids, and were generated in the Gulf of Mexico. The field product, obtained from an offshore drilling well, was processed through an ex-situ stabilization system where oilfield wastes are remediated through dilution and physical isolation of metals and organics in a silica matrix with stabilizing reagents. The exact procedure for stabilization is proprietary information (Swaco Geolograph, New Orleans, Louisiana).
Organic compost was collected in Sulphur, Calcasieu Parish, Louisiana and consisted of decomposed tree and leaf litter. The control sediment for salt marsh conditions (hereafter referred to as estuarine sediment) was collected from an unvegetated salt marsh mudflat in Bayou Chitigue, Terrebonne Parish, Louisiana. For fresh marsh conditions, the control sediment (hereafter referred to as riverine sediment) was collected from exposed alluvial deposits along the Mississippi River bank in Baton Rouge, Louisiana. Both materials were composed primarily of silt and clay in effort to approximate the canal- and bayou-dredged materials com- monly used in Louisiana sediment addition restoration projects.
2.2. Experimental design
The two primary experiments (hereafter referred to as the salt marsh and fresh marsh experiments) were designed similarly, employing a randomized block design with a 4 × 3 factorial treatment arrangement: four levels of substrate type (100% drilled cuttings, 100% compost, 50/50 (v/v) mixture of cuttings and compost, and a control sediment) and three levels of soil amendment (macronutrient (Peters Professional soluble 20-20-20 N-P-K fertilizer), micronutrient (Fe-Mn-Cu-Zn ap- plied through Ciba-Geigy Sequestrene 330 Fe and Tennessee Corporation Es-Min- El soluble fertilizers), and an unfertilized control). The fertilizer applications were split and added at the initiation and midpoint of both experiments for the following rates: 112 kg ha -1 N-P-K, 5.0 kg ha -1 Fe, 1.25 kg ha -1 Mn, 0.625 kg ha-1 Cu, and 0.625 kg ha-1 Zn. The salt marsh experiment began on 4 December 1992 and ended on 2 June 1993 (194 days); the fresh marsh experiment was initiated on 18 July 1993 and terminated on 27 September 1993 (68 days).
A third experiment (hereafter referred to as the fertilizer experiment), which was designed to determine further effects of fertilizer additions on Spartina alterniflora growth, was analyzed as a one-way ANOVA. Treatments included one
500 S. Kelley, 1,4. Mendelssohn /Ecological Engineering 5 (1995) 497-517
substrate type (50/50 (v/v) mixture of compost and drilled cuttings) and three levels of fertilizer amendment (macronutrients plus micronutrients, macronutrients alone, and an unfertilized control), using the same fertilizer types and application rates previously identified. The fertilizer experiment began on 9 February 1994 and ended on 15 May 1994 (95 days).
The three experiments were arranged in completely randomized block designs with five replicates, giving a total of 60 experimental pots for the salt marsh and fresh marsh experiments and 15 pots for the fertilizer experiment. The experimen- tal pots (14 cm diam. X 15 cm ht.), drilled with several holes and lined with 1.5 mm fiberglass mesh screening, were filled with the soil materials. For a source of constant water exchange, the pots were placed within larger pots (22 cm diam. x 18 cm ht.) which were filled with a reservoir of deionized water. Water levels varied one to two inches above and below the soil surface and were replenished every 3 to 5 days depending on evapotranspiration rates. Salt water, prepared with Instant Ocean (Aquarium Systems, Inc., Mentor, Ohio, USA), was maintained at a range of 22-28 ppt for experiments involving Spartina alterniflora. Transplants of Spartina alterniflora were collected from Cocodrie, Terrebonne Parrish, Louisiana for the salt marsh experiment. Nursery-grown Sagittaria lancifolia seedlings (Horticultural Systems, Inc., Parrish, Florida, USA) were used after a 40-day acclimation period in the greenhouse for the fresh marsh experiment. The fertilizer experiment also used transplants of Spartina alterniflora and was conducted in a walk-in growth chamber with the following photoperiod and thermoperiod conditions: 14 h day, 10 h night; 30°C day, 25°C night; average quantum irradiance = 400/~mol m -2 s -1.
2.3. Evaluation of plant growth response
Plant growth was quantified during the three experiments using leaf elongation measurements, cumulative stem height measurements, and biomass accumulation. Leaf elongation was determined by measuring the length of the youngest leaves on the two healthiest plants (if available) in each pot at the beginning and end of a 3-day period. An average of the difference was taken when two plants were measured, and growth was calculated in cm/day.
Cumulative stem heights were determined at the initiation and termination of the salt marsh experiment only, by measuring the height of the tallest leaf of every plant in each pot and calculating the sum. Initial fresh weight was determined for the fresh marsh experiment. Both variables were used as covariates in statistical analysis to account for any variations in initial plant biomass. Plant biomass was determined at the termination of the experiments by rinsing plants thoroughly of soil particles while retaining plant and root tissue in a 1.5 mm mesh sieve. The belowground portion of each plant was clipped from the aboveground plant material, and both were sorted into live and dead categories. In addition, below- ground components of the Spartina alterniflora plants were separated into roots and rhizomes. All portions were dried at 70°C until a constant weight was obtained.
S. Kelley, LA. Mendelssohn /Ecological Engineering 5 (1995) 497-517 501
2.4. Evaluation of substrate physicochemical characteristics in the salt marsh and fresh marsh experiments
Soil interstitial water was collected periodically (days 7, 122, 152, and 179 for salt marsh experiment and days 9, 43, and 66 for fresh marsh experiment) with a perforated plastic tube and syringe as described in McKee et al. (1988). Aliquots of 8 to 10 ml unfiltered water were collected for pH and salinity (salt marsh experiment only) measurements. The remaining water sample was passed through 0.45/zm filters and separated into aliquots for elemental analysis. All samples for elemental analysis were preserved with 15 /zl concentrated HNO 3 (U.S. EPA Method 200.7, 1979), stored in acid-washed glassware, and refrigerated until analysis was done. Measurements of pH were made with a calibrated, combination electrode and an Altex Model 3560 digital pH meter. Salinity was measured with an Atago hand-held refractometer.
Filtered samples were analyzed on a Jarrell-Ash inductively coupled argon plasma-optical emission spectrophotometer (ICP- OES; Atom Comp Series 800) for concentrations of the following elements: Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, and Zn. Additional filtered aliquots, which were frozen immediately upon sampling, were analyzed with an AutoAnalyzer Unit (AAII) for N O 3 - and N O 2 - N (EPA Method 353.2; colorimetric, automated cadmium reduction) and NH4-N (EPA Method 350.1; colorimetric, automated phenate) (U.S. Environmen- tal Protection Agency, 1978).
Soil redox potential (Eh) was measured at two depths (1 and 8 cm) in each pot with four brightened platinum electrodes which were checked before use with a quinhydrone and pH 4 buffer solution. Readings were made on a Cole-Parmer portable millivolt meter using a saturated calomel reference electrode. Corrected Eh values were calculated by adding 244 mV, the potential of the calomel reference electrode. Soil Eh measurements were taken periodically, within a few days of soil interstitial water samples.
Samples of each substrate type were dried and homogenized with mortar and pestle and analyzed for total C and N (Arl Kevex CHN analyzer, Model EA 1108). Following drying and homogenization, additional samples were extracted with concentrated HNO 3 at 130"C for Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, and Zn analysis (ICP-OES).
2.5. Statistical analysis
Data were compiled and analyzed using SAS (SAS Institute, Inc., 1985). For the salt marsh and fresh marsh experiments, statistical differences among the four soil substrates and three fertilizer amendments were determined with analysis of variance (ANOVA) for most parameters measured. Analysis of covariance (ANCOVA) was executed for biomass data. Pairwise comparisons were made with Tukey's studentized range test for balanced data sets, and with the Bonferroni method for unbalanced data sets and ANCOVA procedures (Neter et al., 1990). Data sets for interstitial NO 3 - N and Ni l 4 - N concentrations were in violation
502 s. Kelley, 1.4. Mendelssohn ~Ecological Engineering 5 (1995) 497-517
of univariate assumptions for normality and homoscedasticity (Proc Univariate, SAS, 1985); corrections were made through log transformations. Univariate as- sumptions were valid for all other data sets.
For the fertilizer experiment, statistical differences were determined using ANOVA procedures and single degree of freedom contrasts. Assumptions for univariate analyses were valid for all data sets. Scheffe's statistic was used to test the significance of all F-values at the 0.05 probability level (Neter et al., 1990).
Multivariate analyses (MANOVA) performed on all main effects and interac- tions involving interstitial element concentrations were highly significant for all experiments (p < 0.0001); therefore univariate analyses were performed on indi- vidual elements. Repeated measures analysis was conducted for parameters sam- pled multiple times during the experiments (leaf elongation, interstitial water elements, pH, salinity, and soil redox potential).
3. Results and discussion
3.1. Evaluation of plant growth response
Salt Marsh and fresh marsh experiments: The influence of four substrate types (drilled cuttings, compost, 50/50 mixture compost/drilled cuttings, and control sediments) had significant and similar effects on plant growth of Spartina alterni- flora and Sagittaria lancifolia. Compost substrates generally provided the highest leaf elongation rates, surpassing those of the estuarine sediments and approximat- ing those of the riverine sediments (Fig. la,b). Both species exhibited lowest leaf elongation rates in drilled cuttings, however, when drilled cuttings were combined in a 50/50 mixture with compost, there was a significant increase in plant growth (Fig. la,b). The similar plant responses of the two species to substrate type are consistent with demonstrations that leaf elongation rate is a reliable indicator of treatment effects on plant growth (McKee and Mendelssohn, 1989; Hester and Mendelssohn, 1990; Naidoo et al., 1992).
Differences in plant biomass, including total, aboveground, and belowground, among the four substrate types paralleled those of leaf elongation, with Spartina alterniflora biomass being highest in compost, intermediate in the 50/50 mixture and estuarine sediment, and lowest in drilled cuttings, and Sagittaria lancifolia biomass being highest in compost and riverine sediment, intermediate in the 50/50 mixture, and lowest in drilled cuttings (Fig. 2a,b and Table 1). Biomass results remained significant after adjustment by the covariates (p < 0.0001 for Spartina alterniflora, p < 0.05 for Sagittaria lancifolia).
When compost was mixed with drilled cuttings, the growth of Spartina alterni- flora approximated that in estuarine sediments, but growth of Sagittaria lancifolia was not comparable to that in the highly fertile Mississippi River alluvial sedi- ments. These results indicate that use of drilled cuttings amended with an organic component, such as compost, could be valuable in marsh restoration.
S. Kelley, 1.A. Mendelssohn/Ecological Engineering 5 (1995) 497-517 503
A
o
2.5
2.0
1.5
1.0
O.S
0.0
[] Ora~ C u . ~
• ~ M~ure
r-J Control Sedirnerd
Day 117 Day 150 Day 175 Day 36 Day 61
A
e
==
2.0 (d) Sagittaria • Maclonutdents
6.0 ] a IE CoNroi a 1.5
1.0
0.5
0.0
8.0'
7.0'
5.0'
4.0,
S.O'
2.0'
1.0,
0.0 Ozy ~t7 Day 150 ~ y 175 Day ~ Day s l
Fig. 1. Leaf elongation of Spartina altemillora and Sagittaria lancifolia in response to substrate type (a and b), fertilizer (c and d), and time during the salt marsh and fresh marsh experiments (mean + SE); columns with same letter within each sampling time are not statistically different at the 0.05 probability level. Scales vary for each graph.
The addition of macronutrients, and to a lesser extent micronutrients, had a positive effect on Spartina altemiflora and Sagittaria lancifolia growth in all substrate types. Macronutrient fertilization of Spartina altemiflora plants resulted in significantly greater leaf elongation rates over unfertilized plants for the entire experiment, while the effect of micronutrient fertilization on leaf elongation rate was significant only at the first two sampling times (Fig. lc). The increased leaf elongation rate of Spartina alterniflora at day 150 indicates a dramatic plant response to the second macronutrient fertilizer application, one week prior to growth measurement (Fig. lc). Sagittaria lancifolia leaf elongation rates were significantly affected by application of both macronutrients and micronutrients as compared to unfertilized control treatments, but only at the second sampling time (Fig. ld). Biomass results for Spartina alterniflora and Sagittaria lancifolia also
504 S. Kelley, 1.4. Mendelssohn ~Ecological Engineering 5 (1995) 497-517
35
30
o 2 5
.~ 2 0
15
E 10 .o
'~ 5 I--
0 Com~oa Curfmgs 50/50 Mixture Control
!5"
~0
5
0
5
0
( b ) Sagittaria
a a
Compost Cuttings 50/50 Mixture Control
2 0
o Q.
15 "o
~ 10 E .o_
~ s o
I--
Mao'~uUients Micronutrients Control M~'r~utfi~ts Micr0nutrients Control
Fig. 2. Total biomass accumulation (aboveground, belowground, live, and dead) of Spartina alterniflora and Sagittaria lancifolia in response to substrate type (a and b) and fertilizer amendment (c and d) measured at the end of salt and fresh marsh experiments (mean 5: SE); columns with same letter are not statistically different at the 0.05 probability level. Scales vary for each graph.
demonstrated a significant growth response to macronutrient fertilizer application; however, micronutrient additions did not significantly affect the final biomass of either plant species (Fig. 2c,d). The significant response of Spartina alterniflora to macronutrient fertilization was reflected in all biomass components (shoot, root, rhizome) (Table 1). For Sagittaria lancifolia, a significant response to macronutri- ents was reflected in shoot biomass only (Table 1).
Fertilizer Experiment: Results from the third experiment provided further evidence for the positive effect o f micronutrient additions on Spartina alterniflora growth. In the drilled cut t ing /compos t mixture, total plant biomass and above- ground plant biomass accumulation were significantly increased by the simultane- ous addition of macronutrients and micronutrients over macronutrient fertilization
Tab
le 1
L
ive
bio
mas
s co
mp
on
ents
(g d
wt/
po
t; m
ean
+ S
E)
for
Spar
tina
alte
mifl
ora
and
Sag
ittar
ia l
anci
folia
in
resp
on
se t
o su
bst
rate
typ
e an
d f
erti
lize
r am
end
men
t
Co
mp
ost
D
rill
ed
50
/50
Mix
ture
C
ontr
ol
Mac
ron
utr
ien
ts
Mic
ron
utr
ien
ts
Unf
erti
lize
d cu
ttin
gs
sed
imen
t co
ntro
l
Spar
tina
alte
rnifl
ora
Tot
al
22.9
8+0.
87 a
2
.52
+0
.32
c
7.7
0+
0.8
0 b
7
.65
+ 1
.19
b 15
.20+
2.11
a
13.9
9+ 2
.03
b 13
.02+
2.0
4 b
Sho
ot
15.0
3 +
0.5
6 a
1.51
+ 0
.19
c 4.
99 5
:0.5
5 b
4.61
+ 0
.77
b 10
.44
+ 1
.32
a 9.
56 +
1.3
4 b
9.01
+ 1
.43
b R
oo
t 4.
80+
0.21
a
0.3
9+
0.0
6 c
1
.54
+0
.18
b
1.6
8+
0.2
6 b
2
.63
+0
.47
a
2.3
0+
0.3
9 a
b 2
.29
+0
.43
b
Rh
izo
me
3.1
4+
0.2
4 a
0
.62
+0
.09
b
1.1
6+
0.1
2 b
1
.36
+0
.22
b
2.1
3+
0.3
5 a
2
.13
+0
.33
a
1.72
+0.
21 b
Sagi
ttaria
lan
cifo
lia
Tot
al
13.1
8+0.
70 a
1
.00
+0
.12
c
6.4
2+
0.6
0 b
13
.70+
0.60
a
11.4
7+ 1
.39
a 9
.97
+ 1
.17
b 9
.86
+ 1
.22
b S
hoot
11
.44
+ 0
.20
a 0
.85
+0
.11
c
5.61
+0
.53
b
11.7
7+0.
54 a
10
.21
+ 1
.22
a 8
.94
+ 1
.03
b 8
.57
+ 1
.05
b R
oo
t 1.
74+
0.10
a
0.16
5:0.
02 c
0
.88
+0
.08
b
1.93
+0.
11 a
1
.26
+0
.25
a
1.03
+0.
15 b
1
.29
+0
.18
b
Tot
al b
iom
ass
incl
udes
liv
e ab
ov
egro
un
d a
nd
bel
owgr
ound
. V
alu
es w
ith
the
sam
e le
tter
wit
hin
each
bio
mas
s va
riab
le a
re n
ot
stat
isti
call
y di
ffer
ent
at t
he
0.05
pro
babi
lity
lev
el.
¢ r~
4 .,,4
506 S. Kelley, 1.4. Mendelssohn ~Ecological Engineering 5 (1995) 497-517
0 O .
" 0
t~ tO E .o ..Q
"E t~
70
60
50
40
3 0
20
10
0
Spartina • Macro- plus Micronutrients
a [ ] Macronutrients Alone
Z • Unfertilized Control
b a
b
ab
Total Shoot Root Rhizome
Fig. 3. Live biomass components for Spartina alterniflora grown in the drilled cutting/compost substrate in response to three levels of fertilization during the fertilizer experiment (mean 5: SE). Total biomass includes shoot, root, and rhizome. Columns with same letter within each biomass component are not statistically different at the 0.05 probability level.
alone or the unfertilized control (Fig. 3). No significant effect of either nutrient application was detected in root biomass, nor was any discernible pattern recog- nized for rhizome biomass (Fig. 3). Leaf elongation, likewise, was not significantly affected by fertilizer application (data not shown). However, this lack of response was most likely due to the time of sampling relative to the time of fertilization. In the first two experiments, effects of fertilizer application were most readily detected in leaf elongation rates when growth measurements were taken soon after fertilization. In the third experiment, both sets of leaf elongation measurements were obtained one month after fertilizer application. Simultaneous additions of both macronutrients (N, P, K) and micronutrients (Fe, Mn, Cu, Zn) had a positive, long-term effect on shoot production of Spartina alterniflora which resulted in greater total plant biomass.
Several studies have reported that growth of wetland plants can be limited by certain macro- and micronutrients (Valiela and Teal, 1974; Mendelssohn, 1979; Patrick et al., 1985; DeLaune and Pezeshki, 1988) and that plant growth increases upon addition of limiting nutrients (DeLaune and Lindau, 1990; Hester and Mendelssohn, 1990; Wilsey et aL, 1992). All substrates tested in the present study appeared to be deficient in one or more of the nutrients applied.
3.2. Evaluation of substrate physicochemical characteristics in the salt marsh and fresh marsh experiments
Some of the main factors controlling productivity of Spartina alterniflora and Sagittaria lancifolia are salinity (Linthurst, 1980; McKee and Mendelssohn, 1989),
s. Kelley, 1..4. Mendelssohn /Ecological Engineering 5 (1995) 497-517 507
nutrient deficiencies (Valiela and Teal, 1974; DeLaune and Lindau, 1990), soil pH (Linthurst, 1980), soil mineral content (DeLaune et al., 1979), ion toxicity (Lin- thurst, 1979; Koch and Mendelssohn, 1989), soil waterlogging which can directly affect reduction intensity (Pezeshki et al., 1987; Naidoo et al., 1992) and root oxygen deficiency (Mendelssohn et al., 1981). The differences in plant productivity observed in the present study corresponded with a wide range of environmental parameters represented in each of the substrate types. Relationships between interstitial water pH, soil redox potential, and soluble elemental concentrations in the various substrate types are discussed below.
Interstitial Water pH: Large differences in the growth responses of both marsh plant species among the four substrate types were inversely related to substrate
pH
13
12
11
10
(a) Salt Marsh Experiment ,~ Drilled Cuttings
. . . . . * . . . . 50/50 Mixture
- - " - - - Compost
........... , ....... Control Sediment
9 -
8 -
7 -
, . . . . i i . . . . . . .
i I l I
Day 7 Day 122 Day 152 Day 179
13
12
11
pH 10
9
8
( b ) Fresh Marsh E x p e r i m e n t
n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . g
7
6 m m m
Day 9 Day 43 Day 6 6
Fig. 4. Interstitial water pH for salt marsh and fresh marsh experiments in response to substrate type and time (mean 5: SE).
508 s. Kelley, 1.4. Mendelssohn ~Ecological Engineering 5 (1995) 497-517
interstitial water pH (Fig. 4). Linthurst (1980) showed Spartina alterniflora growth to be lower at pH 8 than pH 6 and speculated that high soil alkalinity levels may directly impact the root membrane or negatively influence the substrate chemistry. This reported decrease in plant growth at high soil pH is consistent with the low growth rates and biomass accumulation found in drilled cutting-grown plants in the present study. Under salt marsh and fresh marsh conditions, the drilled cutting substrate maintained significantly higher interstitial water pH levels than the other three substrates (Fig. 4). The consistently high pH was probably due to potentially high amounts of alkaline drilling fluid additives (NaOH, lime, gypsum) associated with drilled cuttings and the main stabilizing reagent (fly ash) used to process drilled cuttings (relative abundance of fly ash components: SiO2 40-60%; A120 3 15-25%; CaO 20-30%; TiO 2 0-2%; Fe20 3 2-8%; MgO 2-6%).
The addition of compost to drilled cuttings partially counteracted the high alkalinity and resulted in a substrate with pH levels significantly lower than those measured in drilled cuttings but still significantly higher than those in compost or control sediments (Fig. 4). These results are consistent with the findings of Ponnamperuma et al. (1966) and Swarup et al. (1992) who reported a rapid pH decline due to waterlogging in alkaline soils that were amended with organic matter moreso than alkaline soils without organic additions. Both compost and control sediments maintained neutral interstitial water pH levels which were most often not significantly different from one another (Fig. 4).
Soil redox potential: All four substrates developed anaerobic soil conditions in response to waterlogging despite some varying patterns among the substrates (Fig. 5). The initial weakly to moderately reduced state of drilled cuttings may have been caused by low microbial activity due to a physically unfavorable habitat and/or a lack of carbon for microbial metabolism. Over time, however, and especially at a depth of 8 cm, Eh levels in drilled cuttings became strongly reduced and were generally similar to those in the other substrate types (Fig. 5). With the high organic matter content and flooded conditions of the compost and control substrates, microbial populations maintained reduced soil conditions in these substrates at depths of 1 and 8 cm which were generally not different from those in other substrates (Fig. 5). Within this Eh range, NO 3, Mn 4+, Fe 3+, and possibly SO42- are used as electron acceptors for microbial respiration, and their reduced forms are available for plant uptake and accumulation in the soil (Gambrell and Patrick, 1978). Redox potential in the 50/50 mixture compost/drilled cutting substrate was generally low and similar to other substrates in most cases (Fig. 5). An exception occurred at a depth of 8 cm under freshwater conditions (Fig. 5d), where Eh in the 50/50 mixture became strongly reduced ( - 4 0 0 mV) after initial measurement, and was significantly lower than Eh in the remaining three substrate types. It is not clear why this pattern occurred only under freshwater conditions. It has been suggested that additions of organic matter greatly enhance reduction reactions and create strongly reduced conditions (Reddy et al., 1986; Gambrell and Patrick, 1989). However, plant growth rates in the 50/50 mixture substrate were comparable to those of compost-grown plants under freshwater conditions (Fig. lb); thus, the extremely reduced soil status did not appear to inhibit plant growth.
S. Kelley, 1..4. Mendelssohn/Ecological Engineering 5 (1995) 497-517 509
250 "~
200 "
150 - A
:~ 1 0 0 -
~u 50 =
0
-50
-100
- 150
-200
( a ) Salt Marsh Experiment1 cm 250 1
200 -
150 •
100 •
5 0 '
O'
-50,
-100 1
-150 H
-200
(b) Salt Marsh Experiment 8 cm
I | I | I I I I
Day8 Day 119 Day 147 Day 174 Day 8 Day 119 Day 147 Day 174
200
100
0
> -100 E
-200"
-300
-400
-500
(C) Fresh Marsh Experimentt cm
-- Drillsd Cuttings
' - - 50/50 M~ure
o Compost
¢- Contro~ Sediment
I I I
Day 4 Day 46 Day 67
200 "
100 •
O"
- 1 0 0 "
-200"
-300"
-400 '
-50C
(d) Fresh Marsh Experiment8 cm
I I !
Day 4 Day 46 Day 67
Fig. 5. Soil redox potential for salt marsh and fresh marsh experiments at 1 cm and 8 cm in response to substrate type and time (mean + SE). Scales vary for each graph.
Both control sediments remained reduced throughout the experimental periods (Fig. 5) and were generally not different in Eh than the other substrates.
Although soil conditions became reduced in response to waterlogging, the soil interstitial water pH did not approach neutrality in either drilled cuttings or the 50/50 mixture compost/drilled cuttings, as would be expected of alkaline soils (Patrick et al., 1985); we did not observe the p H / E h relationship typical to naturally occurring flooded soils (Bass Becking et al., 1960) in drilled cuttings. Bohn (1969) points out that it is invalid to assume a linear relationship between reactions that determine soil Eh and soil pH in systems containing silicates and other compounds which ale insensitive to changes in redox potential and are active in buffering pH. Eh was therefore not normalized to a constant pH (e.g. Eh7). Since processed drilled cuttings are associated with high relative percentages of
Tab
le 2
T
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arsh
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p)
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S. Kelley, 1.4. Mendelssohn /Ecological Engineering 5 (1995) 497-517 511
Table 3 Salt marsh interstitial water elements averaged over time in response to substrate type (mean 5: SE)
Element Compost Drilled cuttings 50/50 Mixture Control sediment compost/cuttings
Ammonium- 279.01+77.12 a 54.30+ 16.35 b 268.33+50.60 a 116.105:26.59 a Nitrogen (/~ M) Nitrate/Nitrite- 5.32 5:0.44 b 1219.01 5:405.43 a 12.98 5:5.38 b 32.24 5:10.24 b Nitrogen (/zM) Phosphorus (p.M) 49.71 + 6.16 a 6.805: 0.33 b 10.585:0.51 b 37.235:10.65 ab Potassium (raM) 13.14+ 0.37 b 12.245: 0.64 b 11.085:0.44 b 15.995:0.49 a Sodium (raM) 302.495:5.51 b 382.085: 4.00 a 330.875:4.97 b 285.435:4.16 c Calcium (raM) 17.86 + 0.36 b 17.63 + 0.82 b 29.58 5:0.53 a 5.63 5:0.09 c Magnesium(mM) 27.135: 0.57a 0.005: 0 .003b 0.655: 0.00b 30.315: 0.57a Iron (/zM) 69.20 5:12.01 a 0.44 5: 0.06 c 17.62 + 5.60 b 43.69 5:10.23 a Manganese (~M) 82.73 5:2.83 a 0.74 5: 0.12 c 7.63 5:1.86 b 20.20 5:1.11 b Copper (~M) 1.03 5:0.06 b 2.615: 0.38 a 1.125:0.07 b 0.705:0.05 b Zinc (/~M) 6.33+ 2.31 a 1.04+ 0.25 c 1.08± 0.24 c 2.225: 0.42b Aluminum (/tM) 22.41 5:0.35 b 173.58 5:15.83 a 58.08 5:3.67 b 21.96 + 0.38 b Cadmium (~M) 0.28 5:0.03 a 0.03 5: 0.01 b 0.02 5:0.01 b 0.23 5:0.01 a Chromium(/~M) 0.635: 0.01a 0.645: 0.14b 0.115: 0.03b 0.65+ 0.01a Nickel(/z 1.605: 0.19a 4.75+ 0.97a 3.625: 0.73a 1.275: 0.12a Lead(/~M) 0.795: 0.06a 0.255: 0.05b 0.405: 0.00b 0.565: 0.01b
Within each element, means with the same letter are not statistically different at the 0.05 probability level.
silicates (40-60%) and calcium oxide (20-30%), the pH-buffering action of these compounds probably created an insensitivity of substrates involving drilled cuttings to the development of reduced conditions under waterlogging.
Element concentrations, macronutrients and micronutrients: Although some trace metals are known to become mobilized under reduced soil conditions (GambreU and Patrick, 1978), the consistently high pH in drilled cuttings, and to a lesser extent in the 50 /50 mixture of compost /dr i l led cuttings, rendered several trace metals insoluble and therefore unavailable as plant nutrients (Mengel and Kirkby, 1987). Total soil concentrations of P, Mg, Ca, Fe, Mn, Cu, and Al were higher in drilled cuttings than in all other substrates (Table 2). However, interstitial water concentrations of NH4-N, P, Mg, Fe, Mn, and Zn were significantly lower in drilled cuttings than in the compost a n d / o r control sediment interstitial water for both salt marsh and fresh marsh experiments (Tables 3 and 4). The addition of organic matter to drilled cuttings was successful in lowering both pH and Eh which increased the availability of many plant nutrients and improved plant growth in the 50 /50 mixture of compost /dr i l led cuttings. Interstitial water concentrations of NH4-N, Ca, Mg, Fe and Mn were significantly higher in the 50 /50 mixture than in drilled cuttings throughout the salt marsh and fresh marsh experiments (Tables 3 and 4), but the 50 /50 mixture remained significantly lower in P, Mg, Fe, Mn, and Zn than the compost a n d / o r control substrates (Tables 3 and 4). While the compost and control sediment substrates had comparatively low total soil levels of many nutrients (Table 2), their neutral soil pH and lower soil redox potential
512 S. Kelley, I.A. Mendelssohn / Ecological Engineering 5 (1995) 497-517
Table 4 Fresh marsh interstitial water elements averaged over time in response to substrate type (mean 5: SE)
Element Compost Drilled Cuttings 50/50 Mixture Control Compost / Sediment Cuttings
Ammonium- 481.67 + 142.86 a 21.72 + 4.83 c 443.43 + 94.59 a 59.89 + 12.10 b Nitrogen (/~M) Nitrate/Nitrite- 33.58 + 18.81 b 811.12+341.56 a 7.98+ 1.06 b 17.42+ 2.55 b Nitrogen (/~M) Phosphorus(/~M) 217.99 5- 18.56 a 7.76+ 0.94b 16.30+ 1.34 b 5.97± 0.88 b Potassium(mM) 1.28 5: 0.16 a 1.435: 0.07 a 1.815:0.08 a 0.175:0.01 b Sodium(mM) 1.77 + 0.13c 60.82+ 1.30a 36.515: 1.58b 1.35+ 0.07c Calcium (mM) 6.04 5: 0.22 a 1.185: 0.06 c 4.375:0.13 b 1.045:0.04 c Magnesium(mM) 1.87 5: 0.06a 0.025: 0.003c 0.395: 0.04b 0.555: 0.03b Iron (~M) 78.03 5:18.14 a 5.74+ 1.12 c 26.955:7.12 b 75.295:16.83 a Manganese (/zM) 41.11 + 5.57 a 1.865: 0.59 b 7.94+ 1.72 b 49.315:3.13 a Copper (/.tM) BDL c 1.125: 0.20 a 0.265:0.05 b 0.01 + 0.01 c Zinc(/zM) 8.22 + 2.79a 0.795: 0.16b 0.875: 0.20b 1.085: 0.26b Aluminum (/~M) 2.08 5: 0.63 c 1598.05 + 126.93 a 128.79 5:17.41 b 16.05 _+ 1.96 c Cadmium (p.M) 0.0045: 0.004 b 0.03 + 0.01 a BDL b BDL b Chromium(~M) 0.0045: 0.004b 0.975: 0.26a 0.015:0.01 b 0.015:0.01 b Nickel(/~M) 2.10 + 0.39 a 1.245: 0.34 a 2.985:0.72 a 3.095:0.78 a Lead (/~M) BDL b 0.16+ 0.04 a 0.01 5:0.01 b BDL b
BDL indicates below detection limit. Within each element, means with the same letter are not statistically different at the 0.05 probability level.
increased availability of several nutrients over the 50/50 mixture or drilled cuttings (Tables 3 and 4).
Many of the nutrient deficiencies in drilled cuttings and the 50/50 mixture of compost/drilled cuttings appeared to be attributable to pH-related mechanisms and possibly the physical characteristics of drilled cutting sediments. Low concen- trations of ammonium in drilled cutting interstitial water (Tables 3 and 4) could have been due to high adsorption rates of NH~ ions to clay particles (Day et al., 1989). Nitrogen uptake, or perhaps denitrification, was not rapid in drilled cuttings as evidenced by the high nitrate plus nitrite concentrations (Tables 3 and 4). This could be attributed to low plant growth rates or somewhat higher surface redox potentials in drilled cuttings. A major cause of decreased phosphorus availability in soils is the precipitation of soluble phosphates with Fe, Ca and AI (Patrick et al., 1985; Reddy et al., 1986). In addition, calcium phosphate formation is promoted in soils of high alkalinity and Ca concentrations (Mengel and Kirkby, 1987). For the drilled cutting substrate, comparatively high total soil Fe and Ca concentrations (Table 2) most likely precipitated soluble P, given that interstitial water concentra- tions of both Fe and Ca paralleled the trend of decreasing P concentrations over time (Kelley, 1994). Low P concentrations in the 50/50 mixture substrate appeared to be a result of calcium phosphate formation moreso than iron phosphate formation, given the higher availability of Ca in the 50/50 mixture over that of
S. Kelley, I.A. Mendelssohn/Ecological Engineering 5 (1995) 497-517 513
drilled cuttings (Tables 3 and 4) and an increasing trend in interstitial water Fe over time for both experiments (Kelley, 1994). Precipitation with AI did not seem likely since interstitial water AI concentrations remained high during both experi- ments (Tables 3 and 4).
Low interstitial water concentrations of Mg suggested that this element was largely complexed with some drilled cutting constituents and made unavailable to plants (Tables 3 and 4). The availability of Na did not appear to be limited in any of the substrates (Tables 3 and 4). In fact, the high Na levels may have posed a stress to Sagittaria lancifolia (Pezeshki et al., 1987; McKee and Mendelssohn, 1989). Interstitial water salinities (experiment-end means: drilled cuttings = 25.5, 50/50 mixture = 24.4, compost = 23.8, control sediment = 21.8; n - -60) demon- strated that the slightly elevated Na concentrations in drilled cuttings most likely did not influence plant growth of the highly salt-tolerant Spartina alterniflora.
In a neutral soil, Fe and Mn solubility is known to increase upon waterlogging (Gambrell and Patrick, 1978). High concentrations of interstitial water Fe and Mn in compost and control sediments support this hypothesis (Tables 3 and 4). However, in drilled cuttings, high alkalinity dominated these typical waterlogging- induced processes, and both of these metals were rendered unavailable to plants as evidenced by low interstitial water concentrations of Fe and Mn (Tables 3 and 4). Upon addition of compost to drilled cuttings and the subsequent reduction in pH and Eh levels, interstitial water concentrations of Fe and Mn became higher than in 100% drilled cuttings (Tables 3 and 4). These results support the findings of Swarup et al. (1992) who reported an increased availability of Fe and Mn in waterlogged alkaline soils amended with organic matter over alkaline soils not amended.
Zinc and Cu are both reported to bind strongly to humus-rich soils and form insoluble organic complexes (Mengel and Kirkby, 1987). These elements were therefore expected to be more abundant in drilled cuttings than in compost. While this trend was observed for Cu concentrations, the reverse was true for Zn (Tables 3 and 4). Perhaps the high sensitivity of Zn to soil pH levels (Gambrell and Patrick, 1978) was responsible.
Heavy metals: Total soil levels determined that drilled cuttings were the highest of the four substrate types in AI, Cr, and Ni concentrations (Table 2). After exposure to flooded conditions, Cr concentrations in drilled cutting interstitial water decreased to low levels (Tables 3 and 4), and Ni concentrations attained (maximum = 6.6/zM) were likely not high enough to be stressful to plant growth (Mengel and Kirkby, 1987). Concentrations of AI in drilled cutting interstitial water, however, became markedly elevated, especially under fresh marsh condi- tions (Tables 3 and 4). While AI toxicity is generally a concern only in acid soils (Mengel and Kirkby, 1987), potentially high amounts of A1 compound additives associated with the drilled cutting stabilization process (A120 3) could have become "unstable" and potentially stressful to the plants under flooded experimental conditions. The 50/50 mixture of compost/drilled cuttings had somewhat elevated total soil levels of the same metals (AI, Cr, Ni), although not as high as those in drilled cuttings (Table 2). Interstitial water concentrations of Cr and Ni in the
514 S. Kelley, 1..4. Mendelssohn /Ecological Engineering 5 (1995) 497-517
50/50 mixture were similar to those in drilled cuttings and AI concentrations were significantly lower (Tables 3 and 4).
Compost substrates had elevated total soil levels of Pb only, of the heavy metals measured (Table 2). Waterlogged conditions appeared to decrease the solubility of Pb under both saltwater and freshwater conditions (Tables 3 and 4). Formation of any potentially toxic sulfide ions was most likely offset by precipitation with abundant soluble Fe 2+ and Mn 2+ ions. Despite the somewhat elevated total soil levels of AI, Cr, and Ni in estuarine sediment (Table 2), both control sediments had low concentrations of all interstitial water heavy metals (Tables 3 and 4). This may have been due to the capacity of clay particles to precipitate metals (LaBauve et al., 1988; Kotuby-Amacher and Gambrell, 1988).
4. Conclusions
Due to the wide ranges of soil characteristics and abilities to support plant growth represented by the various substrates tested, application of these materials for marsh restoration or creation purposes will depend on the hydrologic and soil physicochemical conditions of the deteriorating site in need of mitigation.
Although the high pH in drilled cuttings had detrimental effects on plant growth during this study, the application of water-based, stabilized drilled cuttings may still be suitable under certain environmental conditions. Areas such as interior "back marsh" habitats, known to be starved of mineral sediment input and therefore containing high percentages of organic matter, would likely benefit from additions of drilled cuttings. Drilled cutting applications would provide three major benefits: (1) input of several essential nutrients known to be abundant in drilled cuttings (2) increased surface elevation to combat local subsidence and sea level rise (3) source of several metals which could be available to precipitate phytotoxins, primarily free sulfides, that tend to accumulate in these low elevation, waterlogged habitats (Linthurst, 1979; Mendelssohn and Seneca, 1980). Any nega- tive impacts of high alkalinity on marsh plants may be offset over time through natural mixing processes of drilled cuttings with the underlying sediments as well as additions of organic matter through plant decomposition.
Although additions of organic compost would be beneficial to most marsh habitats, providing a source of organic energy for plant and microbial communities and contributing to the texture and fertility of existing soils, the application of compost may be most suitable in highly organic marshes. There has been concern over the application of mineral sediments to organic marshes and the possibility of subsequent increased subsidence and deterioration rates. Application of organic compost, with its low bulk density, would eliminate this potential problem. Appli- cation of a drilled cutting/compost mixture would be suitable in most marsh habitats, and, in combination with macronutrients and micronutrients, would likely be comparable to natural marsh sediments in supporting plant growth. The deteriorating marsh would receive benefits from both sediment types: sources of mineral elements and organic matter and increased surface elevation which is crucial to the ability of the marsh to keep pace with relative sea level rise.
S. Kelley, LA. Mendelssohn /Ecological Engineering 5 (1995) 497-517 515
Following further investigation, the use of drilled cuttings and/or compost should be encouraged as an alternative to the current practice of using dredged material as the sole sediment for restoration and creation applications. Both drilled cuttings and compost are currently considered waste products and are unnecessarily occupying landfill space. Plentiful amounts of compost can easily be generated from natural decomposition of grass cuttings, trees, shrubs, and leaf litter to provide a highly organic sediment amendment for use in marsh restora- tion. The abundance of drilled cuttings is weU-documented, as is the cost and effort associated with their disposal. As of 1983, an estimated two million metric tons (d wt) of drilled cuttings were being discharged annually along the US coast, with over 90% occurring in the Gulf of Mexico (National Research Council, 1983). Since drilled cutting applications have not yet been tested in the field, it is difficult to assess the amount needed to successfully increase marsh surface elevation and combat subsidence. However, conservatively speaking, approximately one million barrels of drilled cuttings could potentially raise the elevation of a one square mile marsh three inches (Swaco Geolograph, New Orleans, Louisiana, pers. comm.).
It is the shared opinion of the authors and the State of Louisiana that a feasible economic incentive can be initiated to encourage drilling companies to treat and stabilize drilling wastes, transport them to a mitigation site, and apply them to the marsh surface either using a spray system or bucket dredge equipment (Louisiana Office of the Governor, Coastal Activities Office, pers. comm.). The current treatment and disposal regulations on drilling wastes appear to be costly and stringent enough to promote the success of an incentive program which could possibly involve mitigation credits for drilling companies in exchange for this type of restoration. With the current production rates and availability of both drilled cuttings and compost, in addition to abundant amounts that have been landfilled over past years, there is great potential for restoration of deteriorating marsh systems and creation of new marshes using these materials. However, before any large-scale implementation, these sediment applications must be tested under natural field conditions.
Acknowledgements
We extend our appreciation to Dr. Robert Gambrell for his beneficial com- ments on analytical methods and preliminary reviews of the manuscript, as well as to Dr. Joy Zedler for her constructive comments on manuscript revision. Statistical assistance was provided by Dr. J.P. Geaghan and Dr. R.E. Macchiavelli. This work was supported through funds from the federal Department of Energy. Drilled cuttings were processed and provided by Swaco Geolograph, New Orleans, Louisiana.
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